1. Field of the Invention
This invention relates to an energy recovery technique, and more particularly to an energy recovery circuit wherein energy stored in an inductor is fed to a panel so as to reduce a charge time and enhance energy recovery efficiency. The present invention also is directed to an energy recovery method using the energy recovery circuit.
2. Description of the Related Art
Generally, a plasma display panel (PDP) has a disadvantage of large power consumption. A reduction of such power consumption requires enhancing a light-emitting efficiency and minimizing an unnecessary energy waste occurring in a driving process without a direct relation to a discharge.
An alternating current (AC)-type PDP coats an electrode with a dielectric material to use a surface discharge occurring at the surface of the dielectric material. In this AC-type PDP, a driving pulse has a high voltage of tens of or hundreds of volts (V) to make a sustain discharge of tens of thousand of to hundreds of thousand cells, and has a frequency of more than hundreds of KHz. If such a driving pulse is applied to the cells, a charge/discharge having a high capacitance occurs.
When such a charge/discharge is generated at the PDP, a lot of energy loss occurs at the PDP in proportion to a frequency of the driving pulse. Particularly, if an excessive current flows in the cell upon discharge, then an energy loss is more increased. This energy loss causes a temperature rise of switching devices, which may break the switching devices in the worst case. In order to recover an energy generated unnecessarily within the panel, a driving circuit of the PDP includes an energy recovery circuit.
Referring to FIG. 1, an energy recovery circuit having been suggested by U.S. Pat. No. 5,081,400 of Weber includes first and second switches SW1 and SW2 connected, in parallel, between an inductor L and an external capacitor Css, a third switch SW3 for applying a sustain voltage Vs to a panel capacitor Cp, and a fourth switch SW4 for applying a ground voltage GND to the panel capacitor Cp.
First and second diodes D1 and D2 for limiting a reverse current are connected between the first and second switches SW1 and Sw2. The panel capacitor Cp is an equivalent expression of a capacitance value of the panel. Each of the switches SW1, SW2, SW3 and SW4 is implemented by a semiconductor switching device, for example, a MOS FET device.
An operation of the energy recovery circuit shown in FIG. 1 will be described in conjunction with FIG. 2, assuming that a voltage equal to Vs/2 should be charged in the capacitor Css.
In FIG. 2, Vcp and Icp represent charge/discharge voltage and current of the panel capacitor Cp, respectively.
At a time t1, the first switch SW1 is turned on. Then, a voltage stored in the capacitor Css is applied, via the first switch SW1 and the first diode D1, to the inductor L. Since the inductor L configures a serial LC resonance circuit along with the panel capacitor Cp, the panel capacitor Cp begins to be charged in a resonant waveform.
At a time t2, the first switch SW1 is turned off while the third switch SW3 is turned on. Then, a sustain voltage Vs is applied, via the third switch SW3, to the panel capacitor Cp. From the time t2 until a time t3, a voltage of the panel capacitor Cp remains at a sustaining level.
At a time t3, the third switch SW3 is turned off while the second switch Sw2 is turned on. Then, a voltage of the panel capacitor Cp is recovered into the external capacitor Css by way of the inductor L, the second diode D2 and the second switch Sw2.
At a time t4, the second switch SW2 is turned off while the fourth switch SW4 is turned on. Then, a voltage of the panel capacitor Cp drops into a ground voltage GND.
The energy recovery circuits should satisfy conditions for enhancing a discharge characteristic of the panel, assuring a stable sustain time, and improving an efficiency of energy recovered from the panel. To this end, the conventional energy recovery circuit of FIG. 1 reduces an inductance of the inductor L to accelerate a rising time applied to the panel, thereby improving a discharge characteristic. Also, the energy recovery circuit increases an inductance of the inductor L to enhance energy recovery efficiency.
However, since the conventional energy recovery circuit of FIG. 1 uses the same inductor L at a charge/discharge path. Thus, if the inductor L of the energy recovery circuit is set to a small inductance value to accelerate a rising time, then a peak current is increased to deteriorate energy recovery efficiency. Otherwise, if the inductor L of the conventional recovery circuit is set to a large inductance value to improve an energy recovery efficiency, then a rising time of a voltage applied to the panel is lengthened to deteriorate a discharge characteristic and hence have a difficulty in assuring a sustain time.